Peristaltic pumps are preferred for certain applications where it is desirable to pump measured amounts of a fluid or to pump a fluid through tubing while avoiding contact between pump components and the fluid being pumped. In a typical peristaltic pump system, a length of tubing is contacted by a series of pressure rollers that rotate in a circular path. The pressure rollers contact and progressively compress a flexible pumptube at spaced intervals against a surface or raceway so as to flatten or locally reduce the cross-sectional area of the fluid passageway in the pumptube. Preferably, the cross-sectional area of the fluid passageway is effectively reduced to zero (i.e., complete occlusion) as each pressure roller moves over the pumping section of the pumptube. As the pressure rollers continue to roll over the pumptube, the successive flattened portions expand or return to the original cross-sectional area due to the resilience of the tube which generates a subatmospheric pressure in the fluid passageway to draw the fluid therein.
The efficiency and many operating characteristics of a peristaltic pump depend on the physical and chemical characteristics of the pumptube. The pumptube generally must have a combination of properties including flexibility, resilience, durability, resistance to creasing, and resistance to adverse chemical or physical effects, since the pump may be used to pump diverse materials including acids, alkali, solvents, toxic and sterile liquids. Commercially available peristaltic pumptubes are generally uniformly cylindrical, flexible tubes with a uniform wall thickness which provide a fast recovery rate of the flattened portion to the normal cross-sectional area. Such pumptubes are normally formed from resilient elastomeric materials such as natural rubber, silicone, polychloroprene, and polyvinyl chloride. Such materials, however, have limited resistance to chemical degradation, thereby restricting the use of pumps using such pumptubes to liquids having minimal degradation effects. Fluoroplastic tubing, which has good corrosion resistance, generally has been found to lack resilience and tends to crease in use, thereby limiting the life of such tubing. U.S. Pat. No. 3,875,970 (Apr. 8, 1975) attempted to overcome this problem by providing a pumptube having a thin inner tubular portion of a corrosion resistant material (such as polytetrafluoroethylene) and a thicker outer tubular portion of a resilient elastomeric material (such as silicone, polychloroprene, flexible polyvinyl chloride, natural or synthetic rubber). The overall pumptube remained flexible. Although the design of this pumptube reportably extended the life of the tubing, it has not been as successful as desired and its use in commercially available peristaltic pumps appears to be very limited.
In addition, a variety of pumptubes incorporating various geometric configurations, including multiple layered tubes, have been used in peristaltic pumps. U.S. Pat. No. 3,105,447 (Oct. 1, 1963) used a double layered pumptube where both the inner and outer tubes consisted of rubber or an elastomer. The pumptube design allowed a lubricant to be pumped through the space formed between the inner and outer tubes. German Patent 3,322,843 A1 (published Jan. 3, 1985) also provided a double layered pumptube with a particularly soft and elastic inner layer and an impermeable outer layer. The inner layer could be formed of silicone, natural rubber, soft polyvinyl chloride, polyurethane, or fluoroelastomer; the outer layer could be formed of polyvinyl chloride, polyurethane, fluoroelastomer, and certain polyethylenes. The pumptube was flexible and maintained a circular cross-section in the uncompressed state. European Patent Publication 0,470,33 A1 (published Feb. 12, 1992) provided a flexible pumptube with an elastic reinforcing member or members disposed therein to reduce fatigue failure upon repeated compression and recovery of the tubing. U.S. Pat. No. 5,067,879 (Nov. 26, 1991) provided a flexible, single- or multi-layered pumptube having two longitudinally extending notches or groves in the outer surface. The groves are designed to improve the flexing characteristics of the tubing during compression and recovery. Although providing useful and significant advances in the art, each of these just described pumptubes has significant limitations for use in peristaltic pumps, especially for peristaltic pumps for corrosive and other difficult to handle liquids.
Conventional peristaltic pumps also have significant problems associated with the pumptube having a tendency to be pulled through the pump body by the forces exerted on the pumptube by the pressure rollers. The continuous action of the pressure rollers tends to pull the inlet side of the pumptube into and through the pump housing, thereby increasing the risk of breakage or failure of connection to the liquid source. Invariably, or so it seems, such failures occur most often when the pump is run unattended for several hours, especially in the early hours of the morning. The researcher or technician returns only to find the experiment or analysis ruined because the pump has run dry or otherwise failed. Such failures can be costly and can result in significant delays in the research or analysis program. In the case of medical care, such failures could be catastrophic. Peristaltic pump manufacturers have attempted to overcome this problem by modifying their pumps or pumptubes to provide clamps or other holding devices to counteract the tendency of the pumptube to be pulled through the pump. These devices increase the complexity and cost of the pump and/or pumptubes. Moreover, such devices can themselves fail, thereby allowing the pumptube to be pulled through the pump. Such clamps can also abrade or otherwise damage the pumptube, thereby decreasing its lifetime. It would be desirable to provide a pumptube with a significantly decreased tendency to be pulled into and through the pump without the need for clamps or other holding devices.
The present invention provides an improved peristaltic pump and an improved pumptube which is very different from the pumptubes normally used in such pumps. Whereas prior art pumptubes are constructed of flexible, elastomeric materials which can easily be compressed, the present inventive pumptubes are constructed of relatively hard, rigid materials which can only be compressed by applying significant force. Whereas prior art pumptubes are generally circular in cross-section in the uncompressed state, the present inventive pumptubes are generally flattened and oval-like in the uncompressed state. Whereas the corrosion resistance of fluoroplastic materials could only be used to a limited degree in prior art pumptubes, the present inventive pumptubes allow (and require) use of such fluoroplastic materials while maintaining reasonable pumptube lifetimes. Whereas prior art pumptubes have a tendency to be pulled into and through the pump, the present inventive pumptubes, being rigid, flattened, and shaped to conform to the pumptube passageway, have a significantly reduced tendency to be pulled into the pump. The present inventive pumptubes effectively ignore several design criteria used in conventional pumptubes to provide rigid, relatively non-flexible, shaped pumptubes using fluoroplastic materials.